Liquid delivery pump for liquid chromatograph

ABSTRACT

A liquid delivery pump includes a pump room for transferring liquid, a plunger having one end located in the pump room for moving reciprocally therein for delivering the liquid in the pump room, and a base end, and a crosshead for reciprocal movement situated adjacent to the pump room and having a flat end surface. A ball is attached to the crosshead to contact the flat end surface thereof. The base end is attached to the crosshead so that the plunger rotates freely relative to the flat end surface through the ball.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a liquid delivery pump for a liquidchromatograph, and more specifically, relates to a structure for holdinga plunger moving reciprocally within a pump room.

FIG. 2 is a sectional view of a conventional liquid delivery pump for aliquid chromatograph. In the figure, reference numeral 1 is a pump head;reference numeral 2 is a plunger; reference numeral 3 is a sealingmaterial for allowing the plunger 2 to slide while preventing leak;reference numeral 4 is a pump room formed within the pump head 1;reference numerals 5 and 6 are inlet and outlet for liquid to bedelivered, respectively, and having check valves 5 a and 5 b; referencenumeral 7 is a pump body; reference numeral 8 is a bearing; referencenumeral 9 is a spring; reference numeral 10 is a crosshead; referencenumeral 11 is a cam rotationally driven by a motor not shown in thefigure; and reference numeral 12 is a cam follower that rolls along thecircumference of the cam 11.

A tip side (left side in FIG. 2) of the plunger 2 is inserted into thepump room 4 through the sealing material 3, and a base side (right sidein FIG. 2) thereof is connected to the crosshead 10. The crosshead 10axially supported by the bearing 8 moves reciprocally within the tubularpump body 7 with force imparted by the rotating cam 11 via the camfollower 12 in a forward direction (toward the left side in FIG. 2) andforce imparted by the spring 9 in a retreating direction (toward theright side in FIG. 2). The plunger 2 moves reciprocally within the pumproom 4 accompanying with the movement of the crosshead 10. Accordingly,the pump room 4 is alternately pressurized and depressurized, andassociated operations of the check valves 5 a and 6 a cause liquid toflow from the inlet 5 to the outlet 6, thereby delivering liquid.

The plunger 2A is formed of a material with high hardness, and good wearand chemical resistance such as sapphire. A metal having a surfacecoated with a ceramic film may be used (for example, see PatentReference 1).

FIG. 3 illustrates a connecting structure between the plunger 2 and thecrosshead 10 in more detail. In FIG. 3, the elements same as those shownin FIG. 2 are given the same reference numerals, and their descriptionsare omitted. Reference numeral 15 is a plunger holder. One end of theplunger holder 15 is fixed to the base side of the plunger 2, and theother end thereof is machined to form a spherical end 15 a. The plungerholder 15 is fixed to the crosshead 10 with a screw cap 16, so that theplunger 2 and the crosshead 10 are connected. The spherical end 15 a ofthe plunger 2 abuts against a flat end face 10 a of the crosshead 10with point contact. Accordingly, the plunger 2 freely rotates whilemoving reciprocally along the crosshead 10. With such a structure, it ispossible to prevent grinding or shifting off center between the plunger2 and the sealing material 3 shown in FIG. 2 when the plunger 2 movesand slides reciprocally against the sealing material 3, therebyminimizing wear of the plunger 2 and the sealing material 3.

Patent reference 1: Japanese Patent Publication (Kokai) NO.

In the connecting structure between the plunger and the crossheaddescribed above, it is necessary to machine the spherical end of theplunger holder with a high degree of sphericity to ensure smoothrotation of the plunger, thereby increasing production cost. Moreover,when the plunger is worn out, it is necessary to replace the plungerholder fixed to the plunger together with the plunger, therebyincreasing maintenance cost as well.

In view of the problems described above, an object of the presentinvention is to provide a liquid delivery pump for a liquidchromatograph with production and maintenance costs lower than those ofthe conventional device.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to the presentinvention, a plunger holder is formed in a ball, and a plunger isconnected to the plunger holder with a screw. In other words, accordingto the present invention, a liquid delivery pump comprises a crossheadmoving reciprocally accompanied with a rotational movement of a cam, anda plunger having a tip portion inserted into a pump room via a sealingmaterial and a base portion connected to the crosshead so as to rotatefreely. The ball abuts against a flat end surface of the crosshead at aconnection section between the crosshead and the plunger, and the baseportion of the plunger is screwed in the ball.

In the field of bearings or the like, manufacturing technology has beenestablished to produce a ball with a high degree of sphericity.Accordingly, it is possible to manufacture or obtain a high-quality ballat low cost. According to the present invention, such a ball can be usedas the plunger holder, thereby reducing production cost. In terms ofperformance, the plunger can move freely and follow deformation of thesealing material, thereby reducing wear of the sealing material. As aresult, it is possible to provide a highly durable liquid delivery pumpfor a liquid chromatograph. When the plunger is worn, it is possible toreplace only the plunger, thereby reducing maintenance cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a liquid delivery pump according toan embodiment of the present invention;

FIG. 2 is a schematic view showing a conventional liquid delivery pump;and

FIG. 3 is a detailed view showing the conventional liquid delivery pump.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be explained withreference to the accompanying drawings. FIG. 1 is a schematic viewshowing a liquid delivery pump according to an embodiment of the presentinvention. FIG. 1 corresponds to FIG. 3, and an overall structure of theliquid delivery pump is substantially the same as that shown in FIG. 2.In FIG. 1, the same reference numerals are used for elementsfunctionally same as those in FIG. 3, and descriptions thereof areomitted.

As shown in FIG. 1, in the embodiment, a difference from theconventional pump is that a plunger holder 15 is formed in a ball.Manufacturing technology for a ball with a high degree of sphericity hasbeen established in the field of bearings, and it is possible to produceballs at relatively low cost and high-quality. Such a ball thusmanufactured or obtained is provided with a screw hole 15 b for screwinga female screw to form the plunger holder 15.

The plunger 2 is provided with a male screw 2 a at a base portionthereof, so that the male screw 2 a is screwed into the screw hole 15 b.When the male screw 2 a is screwed into the screw hole 15 b as indicatedby the arrow, the plunger 2 and the plunger holder 15 are connected.

In the embodiment, an operation of the pump constructed as describedabove is basically the same as the conventional pump shown in FIG. 3. Asurface (spherical surface) of the plunger holder 15 abuts against aflat end surface 10 a of the crosshead 10, so that the plunger 2 rotatesfreely. Different from the conventional pump, the spherical body with ahigh degree of sphericity (for example, a ball bearing) is used as theplunger holder 15, so that the plunger 2 moves smoothly and slideswithout grinding against the sealing material 3 shown in FIG. 2, evenwhen the sealing material 3 is slightly off-centered or deformed. As aresult, it is possible to reduce wear of the plunger 2 and the sealingmaterial 3.

Moreover, the plunger 2 is screwed in the plunger holder 15, so that itis easy to replace the plunger 2 when it is worn out. It is necessary toreplace only the plunger 2, thereby reducing replacement cost ascompared with the conventional pump.

The disclosure of Japanese Patent Application No. 2004-088924, filed onMar. 25, 2004, is incorporated in the application.

While the present invention has been explained with reference to thespecific embodiments, the explanation is illustrative and the inventionis limited only by the appended claims.

1. A liquid delivery pump for a liquid chromatograph, comprising: a pumproom for transferring liquid, a plunger having one end located in thepump room for moving reciprocally therein for delivering the liquid inthe pump room, and a base end, a crosshead for reciprocal movementsituated adjacent to the pump room and having a flat end surface, and aball attached to the crosshead to contact the flat end surface thereof,said base end being attached to the crosshead so that the plungerrotates freely relative to the flat end surface through the ball.
 2. Aliquid delivery pump according to claim 1, further comprising sealingmeans attached to the pump room, through which the plunger passes, and acam for reciprocally moving the crosshead.
 3. A liquid delivery pumpaccording to claim 2, wherein said base portion of the plunger isscrewed into the ball.